36 CFR 261.53: Special closures or restrictions.

When provided by an order, it is prohibited to go into or be in any area which is closed or restricted for the protection of:

(a) Threatened, endangered, rare, unique, or vanishing species of plants, animals, birds or fish.

(b) Special biological communities.

(c) Objects or areas of historical, archeological, geological, or paleontological interest.

(d) Scientific experiments or investigations.

(e) Public health or safety.

(f) Property.

(g) The privacy of tribal activities for traditional and cultural purposes. Closure to protect the privacy of tribal activities for traditional and cultural purposes must be requested by an Indian tribe; is subject to approval by the Forest Service; shall be temporary; and shall affect the smallest practicable area for the minimum period necessary for activities of the requesting Indian tribe.